1. Field of the Invention
The present invention relates to the preparation of N-arylsubstituted amides, and, more especially, to the preparation of such amides via reductive N-acylation of nitroaromatic compounds by means of carboxylic acids and carbon monoxide.
2. Description of the Prior Art
The N-substituted amides are known to this art to be particularly useful intermediates for the synthesis of a wide variety of pharmaceuticals and agrochemicals.
It too has been proposed to this art to prepare N-arylsubstituted amides by the reductive acylation of nitroaromatic compounds.
Thus, Bulletin of the Chemical Society of Japan, Vol. 42, 827-828 (1969) describes the conversion of nitrobenzene into acetanilide or propionanilide, respectively, by reacting it with carbon monoxide and acetic or propionic acid, at a temperature greater than 300.degree. C., under initial carbon monoxide pressures, measured at ambient temperature, ranging from 50 to 100 kg/cm.sup.2, and in the presence of nickel tetracarbonyl, dicobalt octacarbonyl or iron pentacarbonyl. Nonetheless, the application of such a process on an industrial scale is largely compromised by the excessively severe operating conditions (temperature and pressure) required.
More recently, an alternative to the above catalyst system has been described, in J. Orgo. Chem., 49, 4451-4455 (1984); it comprises a platinum complex, such as PtCl.sub.2 (PPh.sub.3).sub.2 and tin (IV) chloride or another Lewis acid, such as SnCl.sub.2, FeCl.sub.3, VCl.sub.3, AlCl.sub.3 or ZnCl.sub.2. If the presence of such Lewis acids is indispensable in order to obtain an appropriate acetanilide selectivity, a temperature of at least 180.degree. C. is required to achieve an appreciable conversion of the nitrogen compounds. Furthermore, this conversion is accompanied most frequently by the undesirable co-production of aniline. The required presence of rare and expensive platinum complexes also militates against application of such process on an industrial scale, even though its basic principle is quite valid.
Thus, serious need continues to exist for alternate catalyst systems to those heretofore proposed to this art.